1. Field of the Invention
The present invention relates to an electrochemical cell which has a cathode material comprising a mixture of a cupric halogen compound and a cupric sulfide compound so that a voltage drop will be indicated when the cupric halogen compound has been completely reduced thereby to indicate depletion of the cupric halogen compound and the approaching end of life of the cell.
2. Description of the Prior Art
Heretofore, various electrochemical cells have been proposed which have various cathode material mixtures, such as a cupric halogen compound mixed with a carbon powder, but which do not provide a low impedance cell capable of demonstrating a sufficient voltage drop in order to indicate the approaching end of life of an electrochemical cell.
Examples of such previously proposed electrochemical cells are disclosed in the following U.S. Patents:
______________________________________ U.S. Pat. No. Patentee ______________________________________ 3,450,570 Root 3,542,601 Gabano 3,907,597 Mellors 3,941,612 Steunenberg 3,959,012 Liang et al. 4,410,609 Peled et al. ______________________________________
The Root U.S. Pat. No. 3,450,570 discloses a method of producing a semi-conductive electronegative element of a battery which is produced by heating a finely divided mixture of cupric halide and sulfur in the proportion by weight of one part of cupric halide to 0.03 to 0.5 part of sulfur. The cupric halide may be, for example, cupric fluoride, and cupric sulfide or finely divided copper may be incorporated with some free sulfur into the mixture prior to heating. Accordingly, an electronegative element having a solid compact matrix is produced which has good conductivity, relatively low internal resistance, and which prevents the migration of finely dispersed copper particles from going toward the electro-positive element in a discharge of a battery utilizing such electro-negative elements.
The Gabano U.S. Pat. No. 3,542,601 discloses an electrochemical generator with a non-aqueous electrolyte which includes a halide or sulfide cathode such as a cupric halide or cupric sulfide, and an anode having a strongly electro-negative metal such as an alkali or alkaline earth metal. The non-aqueous electrolyte has a high solvating power and consists of an organic solvent of high solvating power which is a heterocyclic, saturated compound, selected from the group consisting of tetrahydrofuran and tetrahydropyran, together with lithium perchlorate dissolved therein.
The Mellors U.S. Pat. No. 3,907,597 discloses a nonaqueous cell having an electrolyte containing sulfolane or an alkyl-substituted derivative thereof. The non-aqueous cell includes a highly active metal anode, such as lithium, a solid cathode, such as cupric fluoride or copper sulfide, and a liquid organic electrolyte consisting of sulfolane or its liquid alkyl-substituted derivative in combination with a co-solvent.
The Steunenberg U.S. Pat. No. 3,941,612 discloses a cathode composition for an electrochemical cell which includes a negative electrode containing an alkaline metal such as lithium, and an electrolyte of molten salt containing ions of the alkaline metal, and a positive electrode containing a mixture of metallic sulfides. The positive electrode composition is contained within a porous structure that permits permeation of the molten electrolyte and includes a mixture of about 5%-30% by weight cupric sulfide and ferric sulfide.
The Liang et al. U.S. Pat. No. 3,959,012 discloses an electrolyte cell containing a lithium anode, a solid electrolyte of the lithium halide type, and a cathode active material consisting of a mixture of a metal halide and at least one metal chalcogenide. The metal halide is selected from the group comprising lead, silver, copper, antimony, mercury, arsenic, bismuth, chromium, iron, cobalt, nickel, molybdenum and tin. The metal chalcogenide is selected from the group comprising the sulfides, selenides, and tellurides.
The Peled et al. U.S. Pat. No. 4,410,609 discloses an electrochemical cell which includes an anode consisting of lithium, sodium, or a dischargeable alloy of lithium or sodium, and an inert porous cathodic current collector which may be loaded with sulfur, and an electrolyte comprising a solvent mixture which is capable of dissolving a polysulfide in order to attain a concentration of at least 0.01 Mole and to dissolve an electrolyte salt to give a solution of at least 0.1 Mole. The reaction of the anode material with the polysulfide forms a solid electrolyte interphase containing a polysulfide of lithium and sulfur, or sodium and sulfur, so that the concentration of the polysulfide is high enough and the amount of sulfur low enough to result in a predetermined low self-discharge of the cell.
Also it has been proposed to provide in an electrochemical cell a chemical system which will provide a change in electrical potential after the cell has discharged to a predetermined level to provide an indication that the cell is close to the end of its useful life. Examples of such electrochemical cells are disclosed in the following U.S. Patents:
______________________________________ U.S. Pat. No. Patentee ______________________________________ 2,942,052 Bourke et al. 4,144,382 Takeda et al. 4,247,606 Uetani et al. 4,259,415 Tamura et al. 4,293,622 Marincic et al. 4,371,592 Gabano 4,376,810 Takeda et al. 4,388,380 DeHaan et al. 4,418,129 Goebel ______________________________________
The Bourke et al. U.S. Pat. No. 2,942,052 discloses a plurality of series connected cells for determining the state of charge of alkaline batteries. The battery cell includes an anode composed of two or more metals and a cathode whereby a first relative high potential difference is produced with respect to the cathode which maintains its potential until the most electro-negative material in its composition has been used up. Thereafter, the negative electrode exhibits a slightly less negative potential difference until the next less electro-negative component in the series has been consumed.
The Takeda et al. U.S. Pat. No. 4,144,382 discloses an alkaline cell having an active cathode material which is a mixture of monovalent silver oxide and graphite or a compound of which the main ingredient is divalent silver oxide, and a mercury-indium-zinc alloy anode. After almost all the zinc of the anode material is exhausted, a small quantity of indium acts as the anode active material so as to continue to supply current for a period of time but at a lower voltage. This voltage drop indicates that the cell is approaching the end of its useful life.
The Uetani et al. U.S. Pat. No. 4,247,606 discloses a silver oxide battery cell which includes a silver oxide positive electrode and a cell body comprising particles of silver oxide and particles of manganese dioxide, each of the particles having a certain particle size distribution. Prior to complete discharge of the cell, a detectable voltage difference is produced as a result of the particle size distribution to indicate the remaining discharge capacity of the cell.
The Tamura et al. U.S. Pat. No. 4,259,415 discloses a battery comprising a negative active material such as lithium, and a positive active material, such as manganese dioxide, which is part of a primary discharge reaction. In a primary discharge reaction, the negative active material acts through a non-aqueous electrolyte and a precursor such as vanadium pentoxide or lead dioxide and produces a subpositive active material which takes part in a secondary discharge reaction. Accordingly, the approaching end of life of the battery is indicated when the positive active material containing the precursor is consumed and the subpositive active material begins the secondary discharge.
The Marincic et al. U.S. Pat. No. 4,293,622 discloses a step cell comprising a lithium anode, a porous carbon cathode, a vinylchloride depolarizer, and an aluminum chloride/lithium chloride solute. The capacity of the cell is determined by the quantity of active components and is limited by the first component to be exhausted, the vinylchloride electrolyte being exhausted first. Accordingly, a step change in the output voltage of the cell is exhibited prior to full cell discharge in order to indicate that the cell should be replaced.
The Gabano U.S. Pat. No. 4,371,592 discloses a primary cell of high energy density in which the anode active material is an alkaline metal and the cathode active material is sulfur oxychloride which simultaneously acts as an electrolyte solvent and which further includes a dissolved salt and a co-solvent. The co-solvent has a reduction potential relative to the alkaline metal that is less than the reduction potential of the sulfur dioxide which comes from the reduction of the sulfur oxychloride. Accordingly, when the sulfur oxychloride is consumed, the sulfur dioxide is dissolved in the co-solvent and reduced at a potential less than the reduction potential of the oxychloride so that there is a detectable change in its state.
The Takeda et al. U.S. Pat. No. 4,376,810 discloses an alkaline cell which comprises a zinc-indium-mercury alloy anode and in which there is an abrupt lowering of the cell discharge voltage to a distinctly lower voltage level after the zinc constituent has been consumed in order to indicate that the cell is near exhaustion and should be replaced.
The DeHaan et al. U.S. Pat. No. 4,388,380 discloses a lithium cell having a depletion gauge which includes a lithium anode comprising two lithium plates of different thickness and in which an electrical potential on a lead connected to the outer plate falls to zero volts when that lithium plate has been consumed to provide an indication of a predetermined level of discharge of the cell.
The Goebel U.S. Pat. No. 4,418,129 discloses a button type primary electrochemical cell which provides a warning indication toward the end of discharge of the cell and which includes an anode having first and second electrochemically active elements, such as lithium and calcium that have different oxidation potentials. The consumption of the active elements during discharge of the cell results in the establishment of different distinguishable operating voltages for the cell.
As will be described in greater detail hereinafter, the electrochemical cell of the present invention differs from the various electrochemical cells previously proposed by providing an end of life indication of the cell by a change in the voltage potential demonstrated by the cell as a result of partial depletion of the cathode material within the cell. The cathode material is a mixture of a metallic halogen compound and a metallic sulfide compound so that the first voltage potential can be developed between the metallic halogen compound and the anode material within the cell until the metallic halogen compound is depleted so that a second voltage potential different from the first voltage potential can be developed between the metallic sulfide compound and the anode material after the metallic halogen compound is depleted in order to indicate depletion of the metallic halogen compound and the approaching end of life of the cell.